Tanks may be designed in many different configurations, such as spheres, cylinders, cones and shells in general, as well as prismatic shapes. The principle advantage of prismatic shapes is that they nest close to each other, minimising the volume taken up by such tanks. Simple prismatic tanks are far less efficient structurally as they rely on bending action for mobilisation of strength. Shells develop strength through direct tension in the plane of the shell. This develops greater strength for the same amount of material.
A more efficient design of prismatic shapes is to incorporate internal stays (tension beams). By developing tension as the main means of restraining the internal load or pressure, such prismatic staid tanks are comparable to shell shapes in structural efficiency. WO 2006/001711 A2 discloses such tanks and is hereby incorporated by reference.
Apart from having sufficient strength to restrain yielding, the tank structure must also be designed to prevent crack propagation as a consequence of fatigue. The principle concern of such structures is crack propagation at weld locations, as opposed to locations in base metal where crack propagation will progress very slowly or even be arrested.